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Bobcat 225 NT died and will not do anything

09-17-2012, 08:00 AM

Yesterday I was using my Miller bobcat 225 NT as a generator, I had it hooked up to the meter loop of a shop I am building to check some electrical wiring I installed prior to getting electrical service. While actualy making sure some equipment worked in the shop, the Miller Bobcat died (no sputtering or hesitation it just died) while running at high idle, the machine would not do anything when I attempted to start.

The battery is new, I have not checked because it was raining last night when this happened. The fuel tank is full and the oil level is good.

Could this be a fuse, I read that the F-6 fuse when blown the welder would not start. Whould the blown fuse cause the machine to die and not even turnover?

Well, yep, cause ther would be no power going to the coil. nor to the starter.

Why it happened though is a dilema. Did you hook your supply power to test your circuits correctly? ie, it more sounds like you grounded one of the live circuits back to the frame of the machine. That would be the only reason I could think of to take out that fuse.

There just may be further damage besides the fuse, as the DC system doesn't particularly like AC being pumped into it.

Comment

There would have to be a heavy draw on the 12 VDC systom to open F6, like a dead short. I just guessed since you were powering an auxillary circuit when this happened, that that system could be the culprit, or it was simply coincedence.

Never the less report back what you discover. Oh a dead battery, non charging, or low oil would not take that fuse out.

Comment

I did consider the dumping of a heavy auxiliary power load while testing could result in a spike of exciter voltage which could take out (short) flashing diode D4 and backfeed the battery circuit thus blowing F6.

But as you know, F1 should blow first if such were to happen so . . . ???

I agree "a dead battery, non charging, or low oil would not take that fuse out" but a bad regluator could and I wouldn't rule out a battery/ignition circuit wire shorted to ground either.

Comment

I appologize for not getting back and letting everyone know what I found. I found the F6 fuse blown and replaced, the machine fired up when I attempted to strike an arc the machine reved up as usual and I assumed that it was fine. A few days ago my son attempted to use the machine and it would barely strike when attempting to strike an arc. I assume the F1 fuse is blown also, while I am in there are there any suggestions on what to look at also?

One thing I failed to mention in my original post is that it was raining the night the machine quit, is it possible a short was created due to rain? Thanks for the help to this point.

Comment

You really want to inspect the harness plug inbetween the engine starter and generator section. It's VERY likely that the terminals have turns green from corrosion. Clean them and either spray them with the likes of WD-40 or use a DI-Electric grease.

Comment

Well I pulled the top off this evening and the F1 Fuse is blown, duaneb55 what is the best way to check the D4 and the SR2? I know that I need to check resistance with a ohm meter but not sure how I need to do. Also it takes a while to get parts around here, does anyone know if I can get a aftermarket fuse and also the best place to order parts online?

Comment

Well I pulled the top off this evening and the F1 Fuse is blown, duaneb55 what is the best way to check the D4 and the SR2? I know that I need to check resistance with a ohm meter but not sure how I need to do. Also it takes a while to get parts around here, does anyone know if I can get a aftermarket fuse and also the best place to order parts online?

Well, just stick a simple glass fuse in it, a Electronics store will have the ceramic version, a gas station will have the fuse. Don't worry bout the voltage on the fuse, an amp is still an amp. It'll blow all the same.

Comment

Thanks Cruizer, I tried a regular glass fuse, still have weak weld output. The machine speeds up when arc is struck but not enough output to keep arc. Does anyone have any advice on what to check next? I realy need to get this machine running. Thanks for the help.

Comment

Sounds like bridge rectifier SR2 is bad and you're only getting battery voltage (initial exciter current) at the brushes. If you're unsure on how to test SR2 with a VOM (diode setting) - google is your freind.

You'll also need to check D4 the same basic way and I wouldn't doubt it's shorted which would explain the blown F6.